electrodes. And in 1940 a new project of marking of radio valves was worked out , which eliminated this drawback. The most parameters of the system were close to the international one. The first figure approximately showed the heating voltage, the letter in the second place described the basic purpose of the valve or its construction. The figure in the third place did not have a special meaning and then served for division of the valves of the same purpose and construction. For description of the valves' outer design (except the usual metallic ones) another letter was added: "C" - a glass valve of usual size, "M" - glass, mini-sized, "J" - glass, of "acorn" type, etc.

In accordance with the new marking system some valves (in particular, the glass mini-sized ones worked out in 1938) got a new marking. For instance, the valve model SB-242 should be marked 2A1M, the SO-241 - as 2K1M etc. But the new marking was not generally accepted because the radio works continued production of valves with the old marking. Only mini-sized valves of a later design (2K2M, 2J2M) were marked in a new way.

Because by the time there were still many radios in operation using valves of the old 4-Volt glass series our industry produced for some time valves substituting the former types. The names of substituting valves are the following: 4N4S (for SO-118), 4F5S (for SO-122), 4J5S (for SO-124). The inner framework of the tubes

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